API integration for third party online payment

This project is about API integration of an online payment made by a third party website. It is not paypal, or any other known website. It's particulary website that offers this services and we need to implement their procedures on the website we have. We need to save data collected on our website that will contain personal data of client and all necesarry data for the online payment to be done. Based on an unique order id we retrieve from the database after saving the order we will call an authentification procedure that will redirect our client to third party website in a secure enviroment where he can fill its credit card informations. We need to implement these four back and forward procedures of authentification, cashing, canceling and crediting. In the file attached you'll find the procedures need it to implement...